Absolutely fantastic. If you want to play with a feel of OSR but the mechanics of 5e this is your best option in my opinion. The character class advancements, etc are spot-on and feel like B/X. The mechanics themselves are straight elegant applied 5e. If you want modern mechanics with and old-school feel I think this is a great place to start. Also regarding layout and usability, it's absolutely 5 stars.
[5 of 5 Stars!]